WO2007112761A1

WO2007112761A1 - Scheduling radio blocks in a multi-carrier tdma mobile communication system

Info

Publication number: WO2007112761A1
Application number: PCT/EP2006/002972
Authority: WO
Inventors: David Cooper; Mungal Dhanda; Martin Greaves
Original assignee: Matsushita Electric Industrial Co., Ltd.
Priority date: 2006-03-31
Filing date: 2006-03-31
Publication date: 2007-10-11

Abstract

A method of scheduling radio blocks on at least two carriers in a multi-carrier frequency hopping TDMA mobile communication system for uplink transmission by a mobile terminal capable of simultaneous downlink reception on two carriers, comprising the step of assigning N, N being an integer, downlink timeslots on at least a first carrier for use by the mobile terminal, said N downlink timeslots having the same timeslot number on consecutive TDMA frames, the step of assigning M, M being an integer, uplink timeslots on the first carrier for use by the mobile terminal on consecutive TDMA frames, and the step of assigning M uplink timeslots on the second carrier for use by the mobile terminal on consecutive TDMA frames, said uplink timeslots having a different timeslot number than the uplink timeslots on the first carrier, wherein each radio block scheduled for uplink for the mobile terminal consists of 4 timeslots transmitted on the first carrier and 4 timeslots transmitted on the second carrier over a period of 4 consecutive TDMA frames.

Description

SCHEDULING RADIO BLOCKS IN A MULTI-CARRIER TDMA MOBILE

COMMUNICATION SYSTEM

The invention relates to a method for scheduling and transceiving radio blocks in a mobile terminal using at least two carriers of a multi-carrier frequency hopping TDMA mobile communication system. The invention also relates to a corresponding base station for carrying out the scheduling operation and a mobile terminal for transceiving data.

Mobile communication systems have gained large popularity in recent years due to the convenient use for a mobile user. There exist several standardized systems which separate the available physical radio spectrum either by time, frequency or code or a combination thereof.

The known GSM/GPRS system partitions the radio spectrum resource into disjoint carriers, each carrier having a frequency bandwidth of 200 kHz. In turn each carrier is 'time division multiplexed" using a system of recurring timeslots. This is for instance described in 3GPP TS 45.002.

Accordingly, in such a communication system, a timeslot shall have a duration of 3/5200 seconds (« 577 μs) with eight timeslots forming a TDMA frame (« 4,62 ms in duration). At the base transceiver station the TDMA frames on all of the radio frequency channels in the downlink shall be aligned. The same shall apply to the uplink (see 3GPP TS 45.010). Furthermore, at the base transceiver station the start of a TDMA frame on the uplink is delayed by the fixed period of 3 timeslots from the start of the TDMA frame on the downlink.

At the mobile station this delay will be variable to allow adjustment for signal propagation delay. The process of adjusting this advance is known as adaptive frame alignment and is detailed in 3GPP TS 45.010. The staggering of TDMA frames used in the downlink and uplink is in order to allow the same timeslot number to be used in the downlink and uplink whilst avoiding the requirement for the mobile station to transmit and receive simultaneously. The period includes time for adaptive frame alignment, transceiver tuning and receive/transmit switching. Figure 1 shows transmission on a single downlink and single uplink. This is the normal configuration used for circuit switched speech. Note that the GSM system uses frequency hopping, in which the frequencies used to transmit timeslots on both the downlink and uplink change from TDMA frame to TDMA frame. The succession of frequencies is called a hopping sequence. A specific hopping sequence starting at a particular time is referred to as a carrier. A carrier restricted to a particular timeslot is called a "physical channel", hence there are 8 physical channels per carrier.

The GPRS system extends the permitted capabilities as compared with GSM, to allow the mobile terminal to transmit or receive more than one slot in a TDMA frame (multislot operation). This is used for data packet transfer, where (unlike speech) the transfer direction may be asymmetrical, i.e.. for example during web access it is typically the case that more data is sent in the downlink direction. Figure 2 shows an illustration of GPRS multislot operation where the mobile terminal receives three slots and then transmits one slot in each TDMA frame. For simplicity monitoring is omitted.

However, restrictions are also imposed, such as receiving, transmitting, getting ready to receive and getting ready to transmit cannot take place concurrently. Existing conventional mobile terminals only support a single receive and transmit path. By "receive path" and "transmit path" is meant a set of components and entities by means of which receive and transmit operations are carried out in a mobile terminal.

A set of parameters determine the time needed to change from transmit to receive and the time needed to perform measurements and are called turnaround parameters. Typically these parameters are related to the performance of the radio frequency components, for example the synthesizer, which requires time to achieve stabilization. The parameters are typically constrained by baseband performance, for example signal processor speed, and will be called throughput capability parameters.

Recently there have been proposals for evolving the GSM/GPRS system in which the mobile terminals supports two receive paths on the downlink, i.e. simultaneous reception by the mobile handset on two different carriers during the same slot. This is referred to as "downlink dual carrier". An example of this is shown in the figure 3, where for simplicity monitoring is omitted. Receive and transmit operations are mutually exclusive; while transmission is active, reception cannot be performed by either receive path, although operations in preparation for reception, such as retuning, can. Therefore one receive path can share tuning resources, such as the frequency synthesizer, with the transmit path and is called the dependent receive path. The other receive path uses independent tuning resources and is called the independent receive path.

The tuning resources used by the independent receive path are not constrained by the requirements of participating in the transmit operation. Therefore they can be available for other uses.

It is to be noted that according to these recent proposals, however, the timeslots assigned on the carrier and received by an independent receive path correspond to those which are assigned on the other carrier where timeslots are received on the dependent receive path. Thus, according the conventional scheduling operation, resources are wasted in particular on the carrier which could be used as far as not constrained by the transmit operation on the other carrier.

It is seen from figure 3 that there is an asymmetry in data rate. A mobile with the capability of receiving dual carrier on downlink but with a single transmit carrier on the uplink can receive data at twice the data rate that it transmits data. Therefore the data throughput is biased in the downlink direction.

This can be partially alleviated by allowing the mobile to transmit on more than one slot on the uplink, as shown in figure 4, where two consecutive timeslots are used on uplink.

However this solution is unsatisfactory for the following reason: while in each TDMA frame, two independent frequencies are used on the downlink, on the uplink only one frequency is used. Therefore there is less frequency diversity on the uplink and the link performance is reduced.

As illustrated in figure 5, there are two downlink timeslots that cannot be used for transmission of data on the downlink with a legacy mobile terminal. These are firstly the downlink slot immediately before the first transmit slot. Due to timing advance, the downlink slot immediately before a transmit slot overlaps the transmit slot by up to the maximum timing advance (64 bits), so it cannot be used to receive data on the downlink timeslot.

Further, the downlink slot immediately after the last transmit slot cannot be used. If the timing advance were zero, it would require instant retuning from the transmit frequency to the receive frequency. In order to overcome this constraint, it would be necessary to allow the base station to introduce an 'artificial¹ minimum timing offset of 31 symbol periods, i.e. 20% of a timeslot. Then, provided the mobile can switch from transmit to receive in 31 symbol periods, it can use this slot for receive. However, this has the drawback that the usable timing offset range is halved, leading to incompatibilities with legacy networks.

A solution has also been proposed which allows to reduce the time to re-tune between uplink slots. This is illustrated in figure 5, where the time to retune the transmitter is one slot. However it can easily be seen that there is a considerable disadvantage to this solution: the necessary time to retune the transmitter means that uplink slots are wasted, so the maximum uplink data rate is restricted.

In packet switched operation information is transmitted in the form of radio blocks, where each radio block consists of four normal bursts which are transmitted on the same timeslot in a number of successive TDMA frames. This is illustrated in the figure 6, which shows the timeslot assignment used for GPRS, where radio blocks are always transmitted over 4 consecutive TDMA frames. If more than one timeslot is used for uplink or downlink in each frame, then separate and independent radio blocks are sent on different timeslots.

Lastly, a repeating multiframe structure is imposed on TDMA frames, with a repetition period of 52 TDMA frames, as shown in Figure 7. Groups of 4 consecutive TDMA frames within the multiframe structure are used to contain the logical channel containing the GPRS radio blocks labelled BO, Bl.. B11 The other TDMA frames labelled T and X are reserved for signalling and neighbour cell monitoring purposes. The repeat rate of the multiframe structure is 240ms, and each multiframe structure contains 12 radio block periods, so the average radio block TTI (Transmission time interval) is 20ms. This introduces a transmission delay of 20 ms for each radio block resulting from the time the data must be ready for transmission to the time that transmission is completed.

One might wonder why radio blocks are transmitted over 4 TDMA periods, with the consequent delay, rather then (assuming the mobile is capable) using multiple timeslots in a single TDMA frame. For example, why not transmit the block on timeslots 0 and 1 in two consecutive frames, or 0,1 ,2 and 3 in one frame, which would reduce the transmission delay.

The reason this is not done is that mobile communication systems rely on frequency diversity to aid forward error correction. To achieve frequency diversity, systems like GSM use frequency hopping at the TDMA frame rate together with time interleaving and error correction coding. The uplink/downlink frequency pairing used in successive TDMA frames are independent, but within a TDMA frame they do not change. The data included in a single radio block is coded using code with considerable redundancy, and the output of the coding operation is interleaved over the 4 timeslots. If one timeslot is lost, for example due to interference at a specific frequency, there is enough redundant information in the remaining 3 timeslots to recover the information.

For this reason, the transmissions on different timeslots in a single TDMA frame always belong to separate, independent, radio blocks. To attempt to transmit the radio block using more than on slot in a TDMA frame would lead to performance degradation since the frequency diversity gain would be lost (see above referring to Figure 4).

It can be seen from Figure 6 that the length of a radio block is fixed to 4 bursts in each radio block, one burst per TDMA frame. However there are circumstances where it is advantageous to have radio blocks which have more than 4 bursts. This situation arises for instance in the case of Turbo coding operation, which is a well known block coding method which has been proposed for 3GPP communication systems. It is well known that Turbo code performance improves with the length of the coded block. Therefore it would be desirable to increase the number of bursts included in a radio block to values above 4. For example, it has been proposed to use 8 bursts in a radio block radio link parameters, such as carrier to interference ratio or block error rate exhibit better values for Turbo coding when interleaving over 8 bursts rather than 4 bursts, in the case of ideal frequency hopping. In other words, it is more beneficial to send a single radio block interleaved over 8 bursts rather than 2 radio blocks, containing exactly the same total amount of data, each interleaved over 4 bursts, provided that the 8 bursts are on independent hopping frequencies.

At the same time it is desirable not to lengthen the transmission time of a radio block, i.e. to keep it at an average of 4 TDMA frame lengths (i.e. 20 ms), since doing so would have an adverse impact on latency. Moreover, to maintain ideal frequency hopping every burst comprised in a radio block must be transmitted on a different hopping frequency. Lastly, it is desirable for the mobile station to be able to use all possible uplink blocks for transmission, i.e. to change uplink frequency without leaving unused transmission slots due to the need to retune the transmitter frequency.

The object of the invention is consequently to provide a method for scheduling and receiving radio resources on at least two carriers of a multi-carrier frequency hopping TDMA mobile communication system which uses the available radio resources more effectively.

In the light of the above-described problems associated with the conventional assignment schemes, it is the object of the invention to provide a method for scheduling and transceiving radio blocks on at least two carriers of a multi-carrier frequency hopping TDMA mobile communication system that uses the available radio sources more effectively and without latency.

The object is solved by a method for scheduling and receiving radio blocks as set forth in the independent method claims. Further, the object is solved by a correspondingly adapted base station and mobile terminal as set forth by the independent apparatus claims.

The present invention achieves scheduling and transceiving of radio blocks for a dual carrier mobile terminal with an increased number of timeslots assigned on uplink while maintaining the length of 4 TDMA frames for a radio block as defined in a standardized GPRS communication system. Moreover, the time slots are scheduled in a manner that the frequency diversity is maintained due to transmission of bursts on independent hopping frequencies in each TDMA frame. Specifically, the invention allows to schedule a total of 8 timeslots on uplink with 4 timeslots transmitted on each of the dual carriers over a period of 4 consecutive TDMA frames. Thus, for the purpose of turbo encoding, 8 bursts are transmitted over the usual radio block length of 4 TDMA frames, which improves the coding performance at the mobile terminal.

Finally, it is noted that the scheduling scheme according to the invention avoids waste of radio resources and consequently enhances the capacity and performance of the system significantly.

According to a preferred embodiment of the invention, the bursts transmitted in the assigned timeslots each having a frequency on downlink and uplink which changes from TDMA frame to TDMA frame. In this manner, full frequency diversity is maintained, which would otherwise lead to performance degradation.

In conclusion, the invention provides the advantage that radio resources as well as tuning resources may be used in a fairly efficient and resource saving manner.

The invention will be further appreciated from the following detailed description with reference to the accompanying drawings, in which

Figure 1 shows a conventional single slot operation on downlink and uplink of a GSM system,

Figure 2 illustrates multislot operation in a GPRS system,

Figure 3 illustrates dual carrier multislot assignment for a GPRS system,

Figure 4 illustrates dual carrier on downlink and the assignment of 2 timeslots on a single carrier on uplink, Figure 5 illustrates dual carrier on downlink and dual carrier on uplink illustrating the retuning operation in the mobile terminal, Figure 6 illustrates transmission of data packets in form of radio blocks, Figure 7 illustrates a multi-frame structure containing 12 radio block periods of 4 consecutive TDMA frames, Figure 8 illustrates in form of a block diagram the principal operation of a mobile terminal to which the present invention may be applied Figure 9 illustrates in block diagram form the principal operation of a base station to which the present invention may be applied, Figure 10 illustrates dual carrier transmit and receive paths in a mobile terminal according to an embodiment of the invention, Figure 11 illustrates a radio block structure with a timeslot assignment according to a first embodiment of the invention, Figure 12 illustrates an assignment of timeslots according to a second embodiment of the invention, and Figure 13 illustrates a time slot assignment according to a third embodiment of the invention.

Figure 8 is a block diagram for explaining the operation of a mobile terminal which is adapted to carry out the present invention.

A mobile terminal (wireless data communication terminal) 100 allows the bi-directional transfer of data between a base station 200 and an external data source and sink 130.

The base station 200 transmits GPRS signals to the mobile station 100. The GPRS signals are received on the receive antenna 102, and are demodulated to baseband ones by a radio frequency demodulator 108. The radio frequency demodulator 108 delivers the baseband signals to a baseband data receiver 106. The baseband data receiver 106 delivers the received baseband data to a demultiplexer 110. The demultiplexer 110 selects either an NCELL measurement unit 112 or a Layer 2 protocol unit 114 to process the above data, depending on its control input from a timing controller 120.

If the downlink baseband data is destined for the NCELL measurement unit 112, this unit performs adjacent cell signal level measurement, and transmits the resulting information to a Layer 3 protocol unit 116. The Layer 3 protocol unit 116 in turn transmits the data to the base station 200 via the uplink. Downlink baseband data to be used for adjacent cell signal level measurement is routed to the Layer 3 protocol unit 116. The Layer 3 protocol unit 116 separates user plane data and control plane data. The user data is sent to a terminal interface unit 118. The terminal interface unit 118 sends the data to an external data source and sink 130.

Control plane data is used to perform internal control functions. In particular, any GPRS slot allocation frames sent from the base station 200 are used to send parameter data to a slot allocation calculator 128. The slot allocation calculator 128 calculates which TDMA slots shall be used for data reception, data transmission, and adjacent cell signal level measurement purposes. This information is sent to a timing controller setting calculator 126. The timing controller setting calculator 126 in turn reconfigures a timing controller 120 so as to perform each operation of receive preparation, transmit preparation, and adjacent cell signal level measurement at the correct time.

The timing controller 120 is responsible for determining and controlling the timing of the transmission and reception of signals toward the base station 200, and the reception of measurement data. In accordance with the calculation result of the slot allocation calculator 128, the timing controller 120 controls the precise timing and behavior of the radio frequency modulator 122, radio frequency demodulator 108, baseband data receiver 106, baseband transmitter 124, and demultiplexer 110.

User data transmitted from an external data source and sink 130 is accepted by a terminal interface unit 118, and given to a Layer 3 protocol unit 116. The Layer 3 protocol unit 116 multiplexes the data with any protocol control data, and transmits it via a Layer 2 protocol unit 114. The Layer 2 protocol unit 114 in turn transmits the multiplexed data to a baseband transmitter 124. Subsequently, the multiplexed data is modulated by a radio frequency modulator 122, and then is transmitted over a transmit antenna 104.

Figure 9 is a block diagram for explaining the operation of a base station.

A wireless base station 200 allows the bi-directional transfer of data between a plurality of mobile stations 100 and an external Base Station Controller (BSC) 230. Each mobile terminal 100 transmits precisely-timed GPRS signals to the base station 200. The GPRS signals are received on the receive antenna 202, and are demodulated to baseband ones by a radio frequency demodulator 208. The radio frequency demodulator 208 delivers the baseband signals to a baseband data receiver 206. If multiple receive frequencies are used, there is one set of radio frequency demodulator 208 and baseband data receiver 206 per frequency. The baseband data receiver 206 delivers the received baseband data to a multiplexer 210. The multiplexer 210 marks which mobile terminal the data has arrived from depending on its control input from a timing controller 220, and forwards all data received from the mobile terminal 100 to Layer 2 protocol unit 214. The Layer 2 protocol unit 214 maintains a separate context for each mobile terminal 100.

Downlink baseband data to be used for adjacent cell signal level measurement is routed to the Layer 3 protocol unit 216. The Layer 3 protocol unit 216 maintains a separate context for each mobile terminal 100. The Layer 3 protocol unit 216 separates user plane data and radio resource control plane data. User data and radio resource control plane data is sent to a BSC interface unit 218. The BSC interface unit 218 sends the data to an external Base Station Controller 230.

Radio resource control plane data is used to perform internal control functions. In particular, a slot allocation calculator 228 calculates, typically according to the required data rate, which GPRS slots are allocated for each mobile terminal 100. This information is sent to the Layer 3 protocol unit 216. The Layer 3 protocol unit 216 sends allocation information to the mobile terminal 100. This information is also sent to a timing controller setting calculator 226. In addition, other mobile terminal slot allocator 232 receives necessary data from the external Base Station Controller 230 via the BSC interface unit 218, and calculates allocation information for other mobile terminals. This information is also sent to the timing controller setting calculator 226. The timing controller setting calculator 226 in turn reconfigures a timing controller 220 so as to perform each of receive and transmit actions towards each mobile terminal 100 at the correct time.

The timing controller 220 is responsible for determining and controlling the timing of the transmission and reception of signals toward the mobile terminal 100. In accordance with the calculation result of the slot allocation calculator 228, the timing controller 220 controls the precise timing and behavior of the radio frequency modulator 222, radio frequency demodulator 208, baseband data receiver 206, baseband transmitter 224, multiplexer 210, and demultiplexer 234.

User data and control data transmitted from a base station controller 230 is accepted by a BSC interface unit 218, and given to a Layer 3 protocol unit 216. The Layer 3 protocol unit 216 multiplexes the data with any radio resource control data, and transmits it via a Layer 2 protocol unit 214. The Layer 2 protocol unit 214 in turn transmits the multiplexed data to the demultiplexer 234. The demultiplexer 234 provides the data for each mobile terminal 100 on the correct TDMA slot to the correct baseband transmitter 224. Subsequently, the data is modulated by a radio frequency modulator 222, and then is transmitted over a transmit antenna 204. If multiple transmit frequencies are used, there is one set of radio frequency modulator 222 and baseband data transmitter 224 per frequency.

Figure 10 is an illustrative block diagram showing a possible implementation of the baseband receiver/transmitter 106, 124 and demodulator/modulator 108, 122 as shown in figure 4 for a dual downlink carrier mobile terminal which contains two receive paths.

An antenna 10 is time multiplexed to a receive or transmit path via a radio frequency switch 11. When connected to the receive path the signal is routed through a band filter 12 and amplified via a low noise amplifier 13 before being routed into one of two modulators/demodulators or modems 14,15. Each modem contains a frequency synthesizer 16,17 and mixer 18,19. The signal from the mixer is filtered, amplified and digitized for the baseband via the A/D converter 20,21.

Since the system as illustrated uses standard modem components it actually contains two transmit paths, only one of which would be active at a time. In the transmit path the digital signal is converted from the baseband to analog via on of the D/A converters 22,23 and mixed to radio carrier frequency via mixers 24,25, before passing through a passive combining network 26, power amplifier 27 and band filter 28. Only one transmit path is actually used, for example the transmit path from the D/A convertor 22, in which case one receive path shares the use of modem 14 and the other, independent receive path has exclusive use of modem 15. As illustrated in figure 11 , the proposed assignment scheme supports radio blocks comprising 8 bursts on both uplink and downlink. More specifically, transmitted radio blocks are interleaved over 8 bursts at different hopping frequencies on uplink and downlink. In case of downlink, the radio block is transmitted on two carriers and each carrier has 4 bursts interleaved over 4 TDMA frames. In case of uplink, the radio block equally contains 4 bursts on each carrier and interleaved over 4 TDMA frames. It is noted that the timeslots are arranged on uplink at consecutive positions.

According to a second embodiment, the scheduling and transceiving configuration can be used for the transmission of two radio blocks, each having diversity over 8 frequencies on uplink and downlink as illustrated in figure 12. In case of a downlink, two bursts belonging to each radio block labeled B1 and B2 are transmitted during each TDMA frame, each on different carriers. Thus, in total there are transmitted two radio blocks having a total of 16 timeslots on uplink and downlink. As a result, compared with the conventional configuration, the number of interleaving bursts on uplink and downlink is doubled.

The amount of data in the uplink and downlink directions need not necessarily be the same. In figure 13, a third embodiment is illustrated, wherein up to three blocks each interleaved over 8 bursts are sent on uplink, thus having 24 bursts in total. Meanwhile, if not much data needs to be sent on the downlink, only one block using interleaving over 4 bursts in a conventional manner is sent on downlink.

In conclusion, the proposed timeslot assignment scheduling scheme in a mobile station provides a solution for a dual carrier architecture, which permits instant frequency switching on the uplink carrier. It has been demonstrated that a mobile terminal having the resources to perform dual carrier received can use these resources to achieve transmission on successive slots at different frequencies without requiring a specific time gap provision for retuning the transmitter.

Claims

1. A method of scheduling radio blocks on at least two carriers in a multi-carrier frequency hopping TDMA mobile communication system for uplink transmission by a mobile terminal capable of simultaneous downlink reception on two carriers, comprising the steps of:

assigning N, N being an integer, downlink timeslots on at least a first carrier for use by the mobile terminal, said N downlink timeslots having the same timeslot number on consecutive TDMA frames,

assigning M, M being an integer, uplink timeslots on the first carrier for use by the mobile terminal on consecutive TDMA frames,

assigning M uplink timeslots on the second carrier for use by the mobile terminal on consecutive TDMA frames, said uplink timeslots having a different timeslot number than the uplink timeslots on the first carrier,

wherein each radio block scheduled for uplink for the mobile terminal consists of 4 timeslots transmitted on the first carrier and 4 timeslots transmitted on the second carrier over a period of 4 consecutive TDMA frames.

2. The method according to claim 1 , comprising the further step of transmitting radio bursts, each having a frequency on the assigned timeslots on downlink and uplink which changes from TDMA frame to TDMA frame.

3. The method according to claim 1 or 2, wherein the assignment of uplink timeslots to the first and second carrier is contiguous.

4. A method of transceiving radio blocks on at least two carriers in a multi-carrier frequency hopping TDMA mobile communication in a mobile terminal capable of simultaneous downlink reception on two carriers, comprising the steps of: receiving N, N being an integer, downlink timeslots on at least a first carrier for use by the mobile terminal, said N downlink timeslots having the same timeslot number on consecutive TDMA frames,

transmitting M, M being an integer uplink timeslots on the first carrier for use by the mobile terminal on consecutive TDMA frames.

transmitting M uplink timeslots on the second carrier for use by the mobile terminal on consecutive TDMA frames, said uplink timeslots having a different timeslot number than the uplink timeslots on the first carrier,

wherein each radio block transmitted by the mobile terminal on uplink consists of 4 timeslots transmitted on the first carrier and 4 timeslots transmitted on the second carrier over a period of 4 consecutive TDMA frames.

5. The method according to claim 4, comprising the further step of transmitting radio bursts, each having a frequency on the transceived timeslots on downlink and uplink, which changes from TDMA frame to TDMA frame.

6. The method according to claim 4 or 5, comprising the further step of using turbo coding on the bursts contained in the radio block transmitted on the uplink.

7. The method according to one of claims 1 to 6, wherein the scheduling and transceiving operation is carried out by a GPRS system.

8. A base station for scheduling radio blocks on at least two carriers in a multi-carrier frequency hopping TDMA mobile communication system for uplink transmission by a mobile terminal capable of simultaneous downlink reception on two carriers, comprising:

a scheduler adapted to assign N, N being an integer, downlink timeslots on at least a first carrier for use by the mobile terminal, said N downlink timeslots having the same timeslot number on consecutive TDMA frames,

assign M, M being an integer, uplink timeslots on the first carrier for use by the mobile terminal on consecutive TDMA frames,

assign M uplink timeslots on the second carrier for use by the mobile terminal on consecutive TDMA frames, said uplink timeslots having a different timeslot number than the uplink timeslots on the first carrier,

9. The base station according to claim 8, further comprising means for transceiving radio bursts, each having a frequency on the assigned timeslots on downlink and uplink which changes from TDMA frame to TDMA frame.

10. A mobile terminal for transceiving radio blocks on at least two carriers in a multi- carrier frequency hopping TDMA mobile communication system capable of simultaneous downlink reception on two carriers, comprising:

means for receiving N, N being an integer, downlink timeslots on at least a first carrier, said N downlink timeslots having the same timeslot number on consecutive TDMA frames,

means for transmitting M, M being an integer uplink timeslots on the first carrier on consecutive TDMA frames,

means for transmitting M uplink timeslots on the second carrier on consecutive communication TDMA frames, said uplink timeslots having a different timeslot number than the uplink timeslots on the first carrier, wherein each radio block transmitted by the mobile terminal on uplink consists of 4 timeslots transmitted on the first carrier and 4 timeslots transmitted on the second carrier over a period of 4 consecutive TDMA frames.

11. The mobile terminal according to claim 10, further comprising means for transceiving radio bursts, each having a different frequency on the transceived timeslots on downlink and uplink, which changes from TDMA frame to TDMA frame.

12. The mobile terminal according to claim 10 or 11 , being adapted to operate in a mobile communication GPRS system.